This invention relates to a process for the stabilization of activated catalyst masses after the activation of the starting catalyst mass in a gas stream. 2. Statement of Related Art
Particulate catalyst masses, particularly those which have been tabletted, extruded or otherwise pelletized, are widely used on an industrial scale. Such catalyst masses are generally masses of one or more catalytically active components which may contain inert supporting materials. Particularly well known catalysts are metal and metal-support catalysts which are required and used for numerous hydrogenation processes.
Before they are used in the hydrogenation process, catalysts of this type are normally reductively activated by treatment in a reducing atmosphere, more especially in hydrogen or in a gas mixture containing more or less large quantities of hydrogen. The resulting catalyst masses are extremely sensitive to air, as reflected in a distinct reduction in their hydrogenation activity and also in pyrophoric behavior. Accordingly, the production and, in some cases, the storage and transport of highly active catalyst masses such as these, as well as their practical application involves considerable complications and imposes very stringent demands with respect to the need to work in an oxygen-free atmosphere.
It is known in practice that these problems can be overcome in various ways. Thus, air-sensitive, active catalysts can be prepared away from the point of use and the time of use by stabilizing the active hydrogenation catalysts by impregnation with hard fat, hard paraffin, fatty amine or similar compounds. Thus, East German Patent No. 150 390, for example, describes a process for the production of catalysts which consists of pyrophoric nickel metal, optionally on inorganic supports, and which are impregnated with substances melting above 313.degree. K. (40.degree. C). Using this process, the molten suspensions of catalyst and impregnating agent are converted by spraying and simultaneous cooling into a fine grained, free-flowing and air-stable form.
French Patent No. 15 55 015 describes powder-form Raney nickel catalysts which are coated with a protective layer formed by materials having melting points of from 60.degree. to 100.degree. C., more especially hydrogenated vegetable oils, fatty acids or fatty acid salts, glycols, polyfunctional alcohols and organic polymers. These solid layers which prevent the entry of air and which melt at elevated temperatures are said to be applied to the catalyst masses by means of a solvent. Processes such as these for stabilizing activated, particulate catalysts were only used to a limited extent in practice due to the disadvantages involved. These disadvantages are, in particular, the fact that the shaped catalyst elements surrounded by a protective solid increase in volume by comparison with the unimpregnated catalyst elements and, on charging of the reactor for the hydrogenation reaction to be catalyzed, lead to a loss of capacity because the impregnating layers are removed in the course of the hydrogenation process so that the original complete filling intended for the interior of the particular reactor contracts to a partial filling. Unused space unfilled by catalyst mass thus forms in the reactor. This "shrinkage" of the catalyst-protecting layer considerably reduces the potential volume/time yield of the particular process. In addition, the reaction products are contaminated by more or less large quantities of the molten or dissolved impregnating agent, so that the contaminating impregnating agents have to be separated off, at least for the first batches of product.
In view of these disadvantages, catalytic processes of the type used on an industrial scale have resorted to in situ activation of the catalyst charge or filling of a reactor in which, immediately before their use, the particulate catalysts are activated in a reducing gas stream in the reactor from the correspondingly shaped, particulate catalyst masses. This procedure is applied, for example, to copper-chromium and copper-zinc catalysts for the hydrogenation of triglycerides, fatty acid esters and free fatty acids with hydrogen. The particulate catalyst masses containing readily reducible copper oxide are subjected to reduction with hydrogen-containing gas mixtures, as a result of which the copper oxide is converted into finely divided metallic copper. Apart from the fact that the catalyst masses formed are particularly pyrophoric, the shaped elements (tablets, extrudates or pellets) undergo a shrinkage in volume of up to 30%. Accordingly, the catalyst layer which completely fills the interior of the reactor before the beginning of the reducing activation process shrinks by up to 30% during the hydrogenation process, resulting also in an empty reactor volume which is not available to the hydrogenation reaction to be catalyzed. Once again, the potential volume/time yield of the reactor is drastically reduced.